Fabrication of ferromagnetic-semiconductor heteroepitaxial structures using ferromagnetic Ba ferrite films

为了实现高质量的铁磁半导体结构，研究了半导体上磁性氧化层的生长条件。结果如下：1.首次发现在200 ℃下，用（NH_3）_4S_x溶液对GaAs（100）衬底进行硫封端，用电子束蒸发法在GaAs（100）衬底上外延生长了铁磁Fe_3O_4（100）薄膜。在衬底温度高于200摄氏度时沉积的薄膜是多晶的。这与硫的解吸和由此产生的GaAs表面的氧化有关。在450 ℃下，在上述薄膜上生长出了高质量的Fe_3O_4（100）外延薄膜，其面内取向为Fe_3O_4 [100]//GaAs [100]。原子力显微镜和X射线光电子能谱表明，外延薄膜的结晶质量和形貌主要取决于薄膜和衬底之间的晶格失配。在氢端Si（100）和（111）上没有外延生长Fe_3O_4薄膜和α-Fe_2O_3薄膜，其晶格常数与GaAs相似。这些结果表明使用对氧稳定的离子的表面终止对于防止半导体表面在沉积的早期阶段氧化是有效的.研究发现，通过溅射法在α-Fe_2 O_3和α-Al_2 O_3（0001）缓冲层上外延生长了铁磁Ba六角铁氧体（0001）单晶薄膜，以上结果表明，利用Co取代Fe_3 O_3可以实现本研究目标的半导体和强磁各向异性铁磁氧化物的异质外延结构系统。4代替Ba六角铁氧体作为铁磁层和GaAs作为半导体。

In order to realize ferromagnetic-semiconductor structures with high quality, growth conditions of magnetic oxide layrs on semiconductors were investigated. The results are as follows :1.It was found for the first time that ferromagnetic Fe_3O_4 (100) thin films are epitaxially grown on GaAs (100) substrates at 200ﾟC by electron beam evaporation, when the subtrates were sulphur-terminated using an (NH_3) _4S_x solution. The thin films deposited at substrate temperatures above 200ﾟC were polycrystalline. This is associated with desorption of sulphur and resultant oxidization of the GaAs surface. The Fe_3O_4 (100) epitaxial thin films with higher quaslity were grown at 450ﾟC on the above thin films, with the in-plane alignment of Fe_3O_4 [100]//GaAs [100]. Atomic force microscopy and X-ray photoelectron spectroscopy showed that the crystalline quality and morphology of the epitaxial thin films primarily depend on the lattice mismatch between the film and the substrate. No epitaxial growth of Fe_3O_4 thin films and alpha-Fe_2O_3 thin films coccurred on hydrogen-terminated Si (100) and (111) havinb a lattice constant similar to that of GaAs. These results indicate the effectiveness of surface-termination using ions stable to oxygen, for preventing the semiconductor surface from oxidizing in the early stage of the deposition.2. It was found that the (0001) single crystalline thin films of ferromagnetic Ba hexaferrite are epitaxially grown on the buffer layrs of alpha-Fe_2O_3 and alpha-Al_2O_3 (0001) by sputtering.The above results indicate that the heteroepitaxial structure system of a semiconductor and a ferromagnetic oxide with strong magnetic anisotropy which is a goal of this research may be achieved using Co-substituted Fe_3O_4 instead of Ba hexaferrite as a ferromagnetic layr and GaAs as a semiconductor.